The present invention relates to a novel process for preparing cyanohydrin esters. More particularly, the present invention relates to a novel process for the preparation of cyanohydrin esters which requires neither an aldehyde nor a free cyanohydrin as a starting material and which does not involve the formation of free cyanohydrin compounds as intermediates. Specifically, the present invention relates to a process for the preparation of cyanohydrin esters directly from acyl cyanides.
The cyanohydrin esters are important industrial raw materials in that they provide ready access to highly active insecticides. Thus, for example, it is known to react a cyanohydrin ester, such as meta-phenoxybenzaldehyde cyanohydrin acetate with a chrysanthemate, such as ethyl 3-(2,2-dihalovinyl)-2,2-di-methyl cyclopropane carboxylate to form an insecticide of the pyrethroid type, such as NRDC 149, as follows: ##STR1##
It is known to form cyanohydrin esters by reaction of a cyanohydrin and a carboxylic acid chloride or anhydride, i.e.,: ##STR2##
This process, however, requires the use of a free cyanohydrin. The use of free cyanohydrins is objectionable because they are unstable compounds which can release HCN.
Alternatively, it is known to prepare cyanohydrin esters by reacting an aldehyde with an acid chloride in the presence of potassium cyanide, as follows: ##STR3##
This process avoids the handling of free cyanohydrins, and therefore is not as objectionable as the previously mentioned process. It does, however, require the use of an aldehyde. Aldehydes, while not as objectionable as free cyanohydrins from a handling point of view, can be somewhat difficult to obtain and are relatively expensive.
In yet a third process, disclosed in U.S. Pat. No. 4,113,763, cyanohydrin esters are prepared by reacting an aromatic aldehyde with an aliphatic anhydride and then reacting the product with an alkali metal cyanide. This process, however, also requires the use of an aldehyde starting material.
Therefore a need exists for a novel process for preparing cyanohydrin esters which requires the use of neither a free cyanohydrin nor an aldehyde as a starting material, and which does not involve the formation of a free cyanohydrin as an intermediate compound.